Minimally invasive surgical techniques can substantially reduce the risk of injury to patients, in comparison with traditional surgical techniques. The possibility for patient injury remains, however, particularly during the insertion of ports or other instruments through patient tissue to initiate the minimally invasive procedures. The likelihood of patient injury can be reduced by careful selection of an insertion site for the instruments, and definition of a trajectory to a targeted area. However, current surgical planning and navigation systems may not provide sufficient information to allow the selection of an optimal insertion site.